This invention relates to a copper base brazing filler metal alloy which has excellent heat resistance.
High performance heat exchangers have been widely used in order to recover heat energy in waste gas to economize consumption of fuels. Since such kinds of heat exchanger are manufactured by brazing, it is required that the brazing filler metals used is cheap and has a sufficient heat resisting property.
As the heat resisting brazing filler metal, palladium alloys, gold alloys and nickel alloys have been generally known. However, the palladium brazing filler metals and the gold brazing fillet metals are expensive and can not be industrially used, because they include a large amount of noble metals. Further, since the nickel base brazing filler metals are available only as powder states due to their low processing properties, application thereof to places to be brazed takes much time thereby remarkably reducing the productivity.
On the other hand, if a foil brazing filler metal is used, the productivity becomes high, because the brazing filler metal may be merely applied between places to be brazed at assembling. The nickel base brazing filler metals have very excellent heat resisting properties, however, in cases of using the nickel base brazing filler metal for the above noted heat exchangers, the heat resistance thereof is too excellent considering the heat exchangers being operated at a gas temerature of 750.degree. C or less. Accordingly, it has been desired to provide a novel brazing filler metal which is cheap and has a good processing property even if the heat resistance thereof is not so good as that of the nickel base brazing filler metals.
As the result of various studies from such a viewpoint, the present inventors have developed a copper-manganese brazing filler metal and a copper-manganese-nickel brazing filler metal. These brazing filler metals have heat resisting properties for practicable use. Further, a brazing property thereof is good enough, if the brazing is carried out under vacuum.
However, if the brazing is carried out under a certain atmosphere, for example, in hydrogen, such brazing filler metals have defects that oxides of manganese are yielded to cause poor brazing.
Further, such brazing filler metals, which are used mainly for brazing stainless steels etc. have defects that brazed joints will become weak to cause decrease of strength when they are held at an elevated temperature such as 650.degree. C for a long time. It is further desired to improve the heat resisting property thereof because of being somewhat unsatisfactory for it.